This application is based on Japanese Patent Application No. 2000-007900 filed Jan. 17, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a mold assembly for forming an ophthalmic lens or a lens blank, and a method of producing the same using the mold assembly. More particularly, the present invention is concerned with such a mold assembly which is suitably used for forming the ophthalmic lens such as a contact lens or an intraocular lens, or the lens blank from which one ophthalmic lens is produced by effecting a cutting operation on at least one of front and back surfaces of the lens blank, the mold assembly having a structure which assures a high degree of forming accuracy and which is economical to manufacture with relatively inexpensive equipment. The present invention is also concerned with a method of forming the ophthalmic lens or lens blank using the mold assembly, at a reduced cost while assuring a high degree of configurational accuracy of the ophthalmic lens or lens blank to be obtained.
2. Discussion of Related Art
There are proposed various techniques for producing an ophthalmic lens such as a contact lens or an intraocular lens, or a lens blank from which one ophthalmic lens is produced by effecting a cutting operation on at least one of its front and back surfaces, by using a mold assembly consisting of a first mold and a second mold in the form of a male mold and a female mold, or an upper mold and a lower mold. The first and second molds are assembled together to define therebetween a mold cavity having a configuration corresponding to that of the ophthalmic lens or the lens blank. The mold cavity defined when the first and second molds are closed together is filled with a suitable polymeric material to mold the intended ophthalmic lens or lens blank therein.
JP-B-63-36484 and JP-B-3-1125 disclose a method of producing a contact lens by a molding operation, comprising the steps of assembling male and female molds together so as to define a mold cavity therebetween, introducing a polymeric material into the mold cavity, and polymerizing the polymeric material, to thereby provide the contact lens having an intended configuration. In the proposed method, the male and female molds are formed of a resin material rather than a metallic material, for assuring easy removal of the molded contact lens from the molds, and efficient and economical forming of the molds. The male and female molds formed of the resin material undesirably have deteriorated configurational accuracy due to dimensional errors which arise from the shrinkage of the resin material during forming of the resin molds. In this case, the contact lens obtained by using those molds may not have an accurately formed lens surface whose optical portion has an intended optical power. Like ordinary resin products or articles, the resin-made male and female molds are generally produced by high-pressure molding such as injection molding, using metallic dies. The metallic dies used in the high-pressure molding need to have a high degree of mechanical strength, and maintain the original surface condition which is sufficient to provide molding surfaces of the male and female molds with high accuracy of configuration, since the molding surfaces of the molds give the opposite surfaces of the contact lens to be obtained. Such high-pressure molding, however, undesirably and inevitably requires expensive equipment. In addition, the molds are likely to be deformed upon removal or releasing of the molded contact lens therefrom, making it difficult to repeatedly use the molds in subsequent molding operations.
JP-A-10-109316 discloses a mold assembly for forming a contact lens, which assures easy removal of the molded contact lens from a male or a female mold. Described in detail, one of the male and female molds of the mold assembly disclosed in the publication is formed of a metallic material. In the metal mold, the molding surface which gives one of opposite surfaces of the intended contact lens is covered with a release layer which permits the molded contact lens to be easily removed therefrom. When the contact lens is formed by using the mold assembly constructed as described above, the molded contact lens has improved accuracy of surface configuration since the metal mold has dimensional accuracy which is more stable than the resin mold, and assures a sufficiently high degree of hardness for avoiding deformation of the mold and preventing scoring of the mold upon removal of the molded contact lens therefrom. Moreover, the arrangement disclosed in the publication permits the metal mold to be repeatedly used in subsequent molding operations. The above-described mold assembly, however, does not solve the problems of low efficiency and economy of manufacture of such a metal mold.
U.S. Pat. No. 5,524,419 discloses a method and an apparatus for forming a contact lens by a molding operation, wherein a first and a second web each having a suitable width are continuously fed and subjected to a vacuum forming operation for forming a succession of male molds in the form of posterior mold cavities in the first web, and a succession of female molds in the form of anterior mold cavities in the second web. These posterior and anterior mold cavities are formed in the first and second webs, respectively, such that the mold cavities are spaced apart from each other in the longitudinal direction of the first and second webs with a predetermined interval therebetween. After a predetermined amount of a curable lens material is introduced into each anterior mold cavity (as the female mold), the first and second webs are superposed on each other to close the male and female molds together. Thereafter, the lens material in the mold cavities between the male and female molds is polymerized by exposure to a light, to thereby form the intended contact lens in each mold cavity. Subsequently, the first and second webs are separated from each other, and the contact lenses molded in the mold cavities are taken out of the mold cavities.
In forming the male and female molds in the respective first and second webs by the vacuum forming operation which is effected at a lower pressure than in the injection molding, the thickness of the webs in which the male and female molds are to be formed needs to be made small to a certain extent in view of the formability of the male and female molds. If the thickness of the webs is relatively small, the male and female molds formed in the thin webs undesirably tend to be deformed during the molding operation for forming the contact lens. In this case, the contact lens molded in the deformed male and female molds may not have the intended optical characteristics with high accuracy.
It is therefore a first object of the present invention to provide a mold assembly which permits economical manufacture of an ophthalmic lens which exhibits intended optical characteristics with high accuracy, or a lens blank which gives such an ophthalmic lens, while permitting a repeated use of its components.
It is a second object of the invention to provide a method of forming an intended ophthalmic lens or a lens blank using the mold assembly.
The above-indicated first object of the present invention may be attained according to a first aspect of the invention, which provides a mold assembly for forming an ophthalmic lens, or a lens blank from which one ophthalmic lens is produced by effecting a cutting operation on at least one of a front surface and a back surface of the lens blank, the mold assembly consisting of a first mold having a molding surface and a second mold having a molding surface, which first and second molds are assembled together so as to define therebetween a mold cavity having a profile corresponding to that of the ophthalmic lens or the lens blank, the mold cavity being filled with a polymeric material which is polymerized to form the ophthalmic lens or the lens blank, wherein at least one of the first and second molds is a layered mold which is constituted by a composite sheet comprising a metal sheet layer and at least one resin layer which are laminated on each other, the at least one resin layer of the composite sheet providing the molding surface of the layered mold which partially defines the mold cavity.
In the present mold assembly wherein at least one of the first and second molds is a layered mold constituted by a composite sheet in which the metal sheet layer and at least one resin layer are superposed on each other, the layered mold does not suffer from a problem of deteriorated configurational accuracy due to dimensional errors which arise from a shrinkage of a resin material during forming of the conventional resin-made mold. Accordingly, the layered mold which is constituted by each of the at least one of the first and second molds has stable configurational accuracy, so that one of the opposite surfaces of the ophthalmic lens or the lens blank, which is formed by the layered mold and in which the optical potion having an intended optical power is formed, has a high degree of configurational accuracy. The layered mold according to the present invention can be easily formed by effecting a low-pressure press forming or vacuum forming operation on the composite sheet, for instance. Accordingly, the present layered mold can be efficiently and economically formed than the conventional metal mold or the release layer-covered metal mold. In addition, the present layered mold can be formed without requiring expensive equipment as used in forming the conventional resin mold by the high-pressure molding such as injection molding.
In the present layered mold whose molding surface is provided by the resin layer of the composite sheet, the molded ophthalmic lens or lens blank can be easily removed or released from the layered mold which is constituted by each of the at least one of the first and second molds. According to this arrangement, the scoring of the molding surface of the layered mold is prevented when the molded ophthalmic lens or the lens blank is removed therefrom. The presence of the metal sheet layer which is laminated integrally with the resin layer is effective to prevent the layered mold from being deformed upon removal of the molded ophthalmic lens or the lens blank therefrom.
Accordingly, the present mold assembly constructed as described above permits economical production of the ophthalmic lens or the lens blank to which the intended optical characteristics are given with high accuracy. Moreover, the layered mold constituted by each of the at least one of the first and second molds can be repeatedly used in subsequent molding operations.
As described above, the layered mold which consists of each of the at least one of the first and second molds has stable configurational accuracy. When the lens blank formed in the present mold assembly is subjected to a cutting operation on one of its front and back surfaces to form the intended lens surface, the lens blank can be sucked and held with high stability at the other surface by a vacuum chuck having a suction surface whose configuration follows that of the other surface of the lens blank. Accordingly, the cutting operation on the above-indicated one surface of the lens blank can be effected with high stability.
In one preferred form of the above first aspect of the present invention, the composite sheet has a thickness of not smaller than 0.06 mm. The metal sheet layer and the resin layer of the composite sheet preferably have thickness values in a range of 0.05xcx9c0.3 mm and in a range of 0.01xcx9c0.2 mm, respectively. This arrangement permits efficient and economical formation of the layered mold and prevents undesirable deformation of the layered mold upon polymerization of the polymeric material for forming the ophthalmic lens or the lens blank.
In another preferred form of the above first aspect of the present invention, the layered mold is formed by a press forming operation on the composite sheet. According to this arrangement, the layered mold having a configuration which follows that of a press forming surface of a die of a press can be formed with a high degree of configurational accuracy. Therefore, one of the opposite surfaces of the ophthalmic lens or the lens blank, which is formed by the layered mold and in which the optical portion having an intended optical power is formed, can be formed with high accuracy, so that the ophthalmic lens to be obtained is capable of exhibiting the intended optical characteristics. Further, in the subsequent cutting operation on the lens blank, the lens blank can be sucked and held at one of its opposite surfaces which is given by the layered mold, by the vacuum chuck whose suction surface has a configuration following that of the above-indicated one surface of the lens blank.
In still another preferred form of the above first aspect of the invention, the polymeric material in the mold cavity is thermal-polymerized. According to the present arrangement, the polymeric material is polymerized by utilizing a relatively inexpensive heat source such as a heater, whereby the molding operation for forming the ophthalmic lens or the lens blank can be effected at a relatively low cost.
In yet another preferred form of the above first aspect of the invention, the molding surface of the layered mold which provides each of the at least one of the first and second molds, functions as a lens-forming surface which gives a lens surface in which an optical portion of the ophthalmic lens or the lens blank is formed. This arrangement enables the molded ophthalmic lens or the lens blank to have the intended optical characteristics with high accuracy.
In a further preferred form of the above first aspect of the invention, the at least one resin layer comprises a pair of resin layers laminated on opposite surfaces of the metal sheet layer.
In the present composite sheet wherein the metal sheet layer is sandwiched between the resin layers, the opposite surfaces of the composite sheet are provided by the resin layers. Accordingly, in the layered mold formed of the thus constructed composite sheet, the molding surface partially defining the mold cavity is always constituted by either one of the resin layers which sandwich the metal sheet layer therebetween. Unlike the composite sheet wherein only its one of opposite surfaces is provided by the resin layer, the composite sheet of the present arrangement can be readily and easily formed into the layered mold without exercising an utmost care in orientation of the composite sheet in forming the layered mold, resulting in an efficient manufacture of the layered mold.
In a still further preferred form of the above first aspect of the invention, the composite sheet which constitutes the layered mold further comprises an adhesive layer which is interposed between the metal sheet layer and each of the at least one resin layer, for bonding the metal sheet layer and the at least one resin layer together.
The composite sheet wherein the metal sheet layer and the resin layer are firmly bonded together owing to the adhesive layer interposed therebetween can be formed into the layered mold with high efficiency. Further, the present arrangement is effective to prevent the metal sheet layer and the resin layer of the composite sheet from separating away from each other upon molding of the ophthalmic lens or the lens blank, or upon removal of the molded ophthalmic lens or the lens blank from the molding surface of the layered mold constituted by the composite sheet.
The above-indicated second object of the present invention may be attained according to a second aspect of the invention, which provides a method of forming an ophthalmic lens or a lens blank, by using the mold assembly as defined in the above-indicated first aspect of the invention, the method comprising the steps of: assembling the first and second molds together to define the mold cavity therebetween, at least one of the first and second molds being the layered mold whose molding surface partially defining the mold cavity is provided by the at least one resin layer of the composite sheet; polymerizing the polymeric material which fills the mold cavity, to form the ophthalmic lens or the lens blank; separating the first and second molds away from each other; and removing the ophthalmic lens or the lens blank from the first and second molds.
The present method using the mold assembly having the advantages described above permits easy and economical formation of the ophthalmic lens whose optical surface has a high degree of configurational accuracy and which exhibits the intended optical characteristics, or the lens blank that gives such an ophthalmic lens. Since the layered mold of the mold assembly used in the present method can be repeatedly used, the cost for manufacture of the mold assembly is effectively reduced, and the cost for forming the ophthalmic lens or the lens blank is accordingly reduced.